This invention relates to a passive filtration system comprising of a combined particle filter and carbon adsorption filter that is capable of simultaneously capturing chemical and biological warfare agents and other toxic agents, such as toxic industrial chemicals, that does not depend on a detection system for activation, and prevents the spread of chemical and biological agent contamination released in one portion of a commercial building or military facility to other portions of the building or facility. The particle filter traps chemical warfare agent aerosols and biological warfare agents by particle filtration and the carbon filter prevents chemical warfare agents and other toxic agent vapors and gases from escaping by adsorption. The passive filtration system also has the capability to remove all types of indoor air contaminants leading to poor indoor air quality (IAQ) including volatile organic contaminant (VOC) gases, aerosols and particulates normally found in commercial buildings.
This invention also relates to a passive carbon filter with unique water adsorption inhibiting characteristics that can substantially increase the operating life of the filter and which is therefore especially useful in environments where humidity degrades the adsorption performance of the filter.
Carbon has long been used in filters. One problem with carbon as a filtering medium, however, is that it adsorbs water and can quickly lose its adsorption capacity in environments where the relative humidity is not or cannot be controlled. And, even in commercial buildings where the humidity is controlled or in environments where the humidity is naturally low, the useful life of a carbon filter is still not very long.
Carbon regeneration systems are known. See, for example, Cheremisinoff, Paul N., and Ellerbusch, Fred, editors, Carbon Adsorption Handbook, Ann Arbor Science Publishers, Inc. Ann Arbor, Mich., 1978; Cheremisinoff, Nicholas P. and Cheremisinoff, Paul N., editors, Carbon Adsorption for Pollution Control, P.T.R Prentice-Hall, Inc., Englewood Cliffs, N.J., 1993; and U.S. Pat. Nos. 5,565,077 and 5,505,825. But, in many environments, regeneration systems add to the cost and complexity of the filter and, in addition, could cause a concentrated discharge of toxic contaminants, captured by the filter.
In this invention, a long life passive filtration system that is always on-line and which does not require regeneration is disclosed. In one example, a room is equipped with several ceiling tiles including the passive filtration system of this invention. If terrorists set off a canister in the room which releases aerosolized chemical and/or biological warfare agents, the high efficiency particle filter of the system filters out all of the aerosols so that they are not circulated to other rooms in the complex by the heating, ventilation, and air conditioning (HVAC) system of the complex. The pleated carbon filter of the system adsorbs any vapors released from the high efficiency filter due to vaporization of the captured aerosol and other gases that pass through the particle filter. The HVAC system will draw all its return air from within the room through the passive filters. To eliminate air leakage problems through ceiling light fixtures and other room openings and also provide better control of airflow within rooms, a power-vented panel is recommended for use in plenum HVAC returns, making the panel the path of least resistance for the airflow.
It is therefore an object of this invention to provide a passive filtration system.
It is a further object of this invention to provide such a filtration system which is continuously online.
It is a further object of this invention to provide such a passive filtration system which does not require a carbon regeneration subsystem.
It is a further object of this invention to provide such a filtration system which does not require excessive power or any other control input.
It is a further object of this invention to provide such a filtration system which is not disruptive and which does not provide false alarms.
It is a further object of this invention to provide such a passive filtration system which typically has no or few moving parts and which requires little maintenance.
It is a further object of this invention to provide such a filtration system which is easily installed in existing ceiling grids.
It is a further object of this invention to provide such a filtration system which has a very low pressure drop and does not require modifications to existing HVAC equipment.
It is a further object of this invention to provide such a filtration system to minimize air leakage through ceiling light fixtures and other room openings and allow all of the airflow through the filtration panel.
It is a further object of this invention to provide such a filtration system which is highly visible so that unauthorized removal or tampering thereof can be immediately detected.
It is a further object of this invention to provide such a filtration system which has a life expectancy of at least five years under background concentrations of indoor air contaminants including VOCs, aerosols, particulates and other allergens, normally found in commercial buildings.
This invention results from the realization that a pleated carbon felt filter treated with a silane based organofunctional hydrophobic solution inhibits the adsorption of water thereby increasing the adsorption capacity of the pleated carbon filter especially in high relative humidity environments. The hydrophobic solution is selected so that is does not decrease the adsorption capacity of the carbon filter and so that it can thus filter out harmful vapors. The carbon felt material may also be treated with reactive metals to enable the treatment of various acid and alkaline gases not otherwise treated by unimpregnated carbon fiber material.
This invention features a filter system for passive filtration comprising a housing with an intake and an outlet, a pleated carbon filter disposed between the intake and the outlet for filtering out vapors entering the intake, and a hydrophobic solution dispersed about the pleated carbon filter to inhibit adsorption of water thereby increasing the adsorption capacity of the pleated carbon filter especially in high relative humidity environments. Preferably, the hydrophobic solution is selected so that it does not decrease the adsorption capacity of the carbon filter. One such solution is a silane composition.
In one example, the pleated carbon filter is made of carbon felt material, there is approximately one pleat per inch and the carbon felt material is approximately 5 mm thick. In the same example, the housing is approximately 4 inches deep and each pleat is approximately four inches high.
Further included may be one or more reactive metals disposed in the carbon filter to render toxic gases entering through the intake non-toxic. Typical reactive metals include copper, zinc and molybdenum. In one embodiment, a high efficiency particle filter is disposed adjacent the intake opening of the housing for filtering aerosols before they enter the intake, one or more lower efficiency filters are located adjacent the high efficiency filter, and a blower is disposed at the outlet of the housing to increase the flow through the intake.
This embodiment is useful in a room with a plurality of tiles forming a ceiling and wherein select tiles are replaced with the passive filters of this invention: a housing with an intake and an outlet, a pleated carbon filter made of carbon felt material disposed between the intake and the outlet for filtering out vapors entering the intake, and a hydrophobic silane solution dispersed in the pleated carbon felt material filter to inhibit adsorption of water by the carbon thereby increasing the adsorption capacity of the pleated carbon filter especially in high relative humidity environments. The housing may be 2 feet wide by 10 inches deep and 2 feet long or 4 feet long. A high efficiency particle filter may be disposed adjacent the intake opening of the housing for filtering aerosols before they enter the intake and one or more lower efficiency filters are typically located adjacent the high efficiency filter. A blower disposed at the outlet of the housing of selected filters increases the flow therethrough and generates a pressure above the ceiling greater than the pressure below the ceiling.
This invention also features a method wherein a pleated carbon filter disposed between the intake and the outlet of a housing is treated with a hydrophobic solution dispersed about the pleated carbon filter to inhibit adsorption of water thereby increasing the adsorption capacity of the pleated carbon filter especially in high relative humidity environments. The hydrophobic solution is selected so that it does not decrease the adsorption capacity of the carbon filter. One such solution is a silane composition.